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December 06, 2017

Long Term Evolution Unlicensed (LTE-U) was intended as a way to get unlicensed LTE out into the market without waiting for the 3GPP, which governs LTE, to build License Assistance Access (LAA) into the next release of the standard.

Although LTE-U was designed to work in any spectrum band, 5GHz was set as the initial target due to large swaths of available bandwidth. But 5GHz is already a very crowded space with cable, Wi-Fi, vehicle-to-vehicle (V2V) dedicated short-range communications (DSRC) and sub-6GHz 5G. Moreover, LTE-U has no listen before talk (LBT) capability, so the uneven regulatory landscape is pushing the market toward LAA.

Is LAA the way forward?

LAA is the 3GPP’s effort to standardize the operation of LTE in the Wi-Fi bands, using the LBT contention protocol (mandated in Europe and Japan).

LAA has two big advantages over LTE-U:

It includes an LBT feature to help overcome what critics call LTE-U’s biggest flaw: that it may start transmitting even if another radio is using the same channel

It is part of the official LTE standard, which carriers count on to make sure their systems work and can grow into the future; service providers like their network equipment to meet global standards

In addition to LBT regulation, LAA meets other regulatory requirements such as transmit power spectral density (PSD) and the channel occupancy bandwidth requirement in Europe. It also preserves coexistence and fair sharing with other unlicensed technologies including Wi-Fi.

The upgrade from LTE-U to LAA is straightforward software

Half of the large service providers worldwide are embarking on an LAA journey this year. In our September 2017 Small Cell Strategies and Vendor Leadership Service Provider Survey, we asked respondents if they currently use or plan to use any unlicensed aggregation technology. We found that 50 percent of respondents had plans to deploy LAA by year’s end. Another group accounting for 14 percent had plans to deploy LWA (LTE + Wi-Fi link aggregation). The strongest traction will occur in North America and parts of Asia Pacific, which are the early LTE adopters and are currently upgrading some of their LTE outdoor small cells with 4x4 MIMO (multiple input, multiple output), 256QAM (quadrature amplitude modulation) and LAA.

Unlicensed technologies will play a key role

Wi-Fi has very long and powerful legs, and mobile broadband badly needs LTE and Wi-Fi together. So far they get along together for LAA, but the next steps leading to enhanced LAA (eLAA) look cloudier.

The unabated need for capacity means that unlicensed spectrum must be harnessed to support LTE services, and later, 5G.

In the US, AT&T, T-Mobile US and Verizon have already jumped on the LTE‑U/LAA bandwagon; it’s an easy software upgrade to their small cells as long as devices are available. The world will follow with LAA rollouts in Asia (SK Telecom) and Europe (Vodafone).

The different LTE-U options enhance the operational model and overall business case for small cells as part of network densification strategy. Meanwhile, the use of unlicensed spectrum by LTE is not without controversy. Wi-Fi is a contested spectrum, so there is potential for friction. The lack of coexistence rules could delay widespread implementation. And standards are still being finalized; when adopted, they could give the market an injection of activity.

The next steps leading to eLAA are less clear

eLAA, which consists of adding an uplink to LAA, will be more challenging with increases in radio frequency (RF) front-end content as OEMs add additional complexity to the cellular radio to accommodate this requirement.

Moving forward with aggregation techniques, the WLAN scenario that’ll be adopted first remains unclear. LWA provides considerable technology and market advantages as it enables tight convergence and integration between a new network of access points and a small cell architecture; it bodes well for service providers that operate both cellular and established Wi-Fi networks.

But what about legacy Wi-Fi networks? LWIP is the answer. LWIP operates in either LTE or Wi-Fi and has strong advantages over LAA and LWA. It will not, however, be carried into 5G because the concept in general is very different.

Unlicensed spectrum and WLAN interworking will continue to play a major role in 5G. The 3GPP new radio (NR) standard already includes requirements for tight interworking with WLAN and licensed assisted operations such as non-standalone NR (NSA-NR) and standalone NR (SA-NR).

Beyond current LAA rollouts, it is still early to predict which WLAN scenarios will actually be standardized and deployed with 5G. However, we believe that at least LWA, and eLWA already, provide a solid networking foundation to enable 5G/WLAN interworking.